There are a variety of optical communication system applications that utilize optical waveguides of varying lengths, or simply require the use of relatively long waveguides. For example, optical delay lines are typically based on configurations having two separate optical waveguide paths, with one path having an “optical path length” exactly out of phase with a second path. Optical interferometers are based on similar phase differences. Optical amplifiers based on Raman amplification require waveguides on the order of tens of meters in order to provide a sufficient longitudinal extent for interaction between the signal and pump.
An arrayed waveguide grating (AWG) is one well-known type of component that utilizes a set of optical waveguides of different lengths (from “shortest” to “longest” disposed in an array configuration). The AWG works by splitting incoming light among an array of many waveguides, each with an incrementally longer optical path. The array of waveguides is then recombined in a slab waveguide, where the light from each path interferes such that different spectral slices focus to different spatial locations. By placing a set of waveguides at the focal plane, each spectral slice can be collected by a separate waveguide.
An AWG is commonly used in wavelength division multiplexing (WDM) applications and is preferably fabricated using photonic lightwave circuit (PLC) technology. PLC serves to integrate various optical components and devices in a functional module for a specific application. While PLC technology is able to create patterns of waveguides (such as arrays) on a silicon substrate, the waveguides fabricated in this platform are relatively large and unable to bend around a tight curve without creating significant optical signal loss (i.e., a tight bend tends to disrupt the signal confinement properties of an optical waveguide and allows a portion of a propagating light beam to be directed away from signal path). Because of this, AWGs fabricated using PLC technology can be rather large devices (multiple square centimeters). Moreover, as the number of channels is increased (or as the bandwidth of each channel is decreased), the resultant size of the device quickly grows.
There are also additional minimum-size restrictions imposed by the waveguide-to-waveguide length differential ΔL in the array and the desired number of waveguides in the array, as well as the focal lengths required in the input and output slabs. Other factors may also play a role in thwarting attempts to shrink AWG device designs. It would be desirable if some of these factors could be overcome to enable smaller AWGs.